The invention relates to an optical image projector, and more particularly, to such projector which utilizes an array of optical focussing elements which projects an erect positive image of unity magnification, for projecting the image of an object onto an image receiving surface which is nonparallel to the plane of the object.
An array of optical focussing elements, as termed a fiber lens array, comprises a plurality of converging light transmitting members, formed of light transmitting material of a rod shape in which the refractive index varies from the center thereof toward the periphery, for projecting an erect positive image of unity magnification. Such array is offered on the marketplace in the tradename of Selfoc lens array (manufactured by Nippon Sheet Glass Co.), and is commonly and extensively in practical use. Such array of optical focussing elements will be referred to hereinafter as a fiber lens array.
In the use of such a fiber lens array, the plane of an object to be projected and an image receiving surface are generally disposed so as to be perpendicular to the optical axis of a lens, in a similar manner to the use of a spherical lens. An essential part of an electrophotographic copying machine which employs an optical image projector of such an arrangement is illustrated in FIG. 1. The plane of an object to be projected is defined by an original receptacle 1 which comprises a glass pane. An original 2 is placed on the receptacle and is illuminated by an illumination unit 3 including a lamp 3a and a reflector 3b. A fiber lens array 4 projects an erect positive image of unity magnification of the original onto a photosensitive drum 5 which constitutes an image receiving surface. Where the fiber lens array 4 is used, the distance Tc between the original surface v and the image receiving surface z is small, normally 80 mm or less, thus leaving little freedom to change its arrangement. For example, when the original surface v is horizontal, it is necessary that the array 4 be disposed so that its optical axis P coincides with a vertical line Q passing through the center O of the drum 5.
While the arrangement shown in FIG. 1 provides an optimum optical performance, if it becomes necessary to transpose the array 4 to another location in consideration of some other member which must be disposed around the drum 5, there is little freedom to allow for this. By way of example, assume that it becomes necessary to dispose the array 4 so that it be disposed along a straight line which is at an angle .alpha. from the vertical line passing through the center O of the drum 5. To achieve the optimum focussing condition, the original receptacle 1 must also be disposed at an angle of .alpha. with respect to the horizontal (see FIG. 2). The optimum focussing condition cannot be satisfied if the receptacle 1 is left in its horizontal disposition.
To avoid the restriction imposed upon the arrangement as mentioned above, it is known to interpose a reflecting surface such as a mirror or a prism in the optical path of the array, thereby deflecting the optical path. By way of example, Japanese Laid-Open Patent Application No. 92,740/1975 discloses an arrangement as shown in FIG. 3 in which a single reflecting mirror 6 is interposed between the array 4 and the drum 5 to fold the optical axis at right angles. This arrangement suffers from the disadvantages that an inversion of the image occurs as a result of the presence of the mirror 6 and that the addition of another optical element in the optical path makes the arrangement susceptible to the influence of a marring. In particular, with an electrophotographic copying machine which employs dry developer and in which the scattering of toner is likely to occur, the influence of marring cannot be neglected. The inversion of the image can be overcome by disposing a pair of reflecting mirrors 6a and 6b on the opposite sides of the array 4, as shown in FIG. 4. However, this arrangement presents other difficulties in that the arrangement is more susceptible to the influence of a marring and that the closeness between the original surface v and the image receiving surface z makes the disposition of an illumination unit difficult.
While it may be contemplated to use a flexible fiber lens array in order to overcome the described disadvantages and difficulties by one effort. However, such array is very difficult to manufacture and is very expensive, presenting a great difficulty in practical use.